1. Field of the Invention
This invention relates to a vehicle transmission, and more particularly to a vehicle transmission for transmitting a power output from an engine unit to a wheel.
2. Description of the Related Art
Referring to FIG. 1, a first conventional vehicle transmission 1 includes a box 11, a driving unit 12 disposed in the box 11, and a speed-changing unit 13 disposed in the box 11 and driven by the driving unit 12. The box 11 has a housing portion 111 and a cover portion 112 interconnected removably.
The driving unit 12 includes a driving pulley (not shown) disposed in an engine unit (not shown), an output shaft 120 journalled in the box 11, a driven pulley 121 sleeved fixedly on the output shaft 120, and a transmission belt 122 trained on the driving pulley and the driven pulley 121 for transmitting a power output from the engine unit to the output shaft 122.
With further reference to FIG. 2, the speed-changing unit 13 includes an axle 131 disposed parallel to the output shaft 120 and extending outwardly of the cover portion 112, a rotating shaft 132 disposed rotatably between and parallel to the output shaft 120 and the axle 131, a first gear 133 sleeved fixedly on the output shaft 120, a second gear 133′ sleeved fixedly on the axle 131, a third gear 134 sleeved fixedly on the rotating shaft 132 and meshing with the first gear 133, and a fourth gear 133 formed integrally on the rotating shaft 132 and meshing with the second gear 133′. A line (L) extends through the rotating axes of the first gears 133, and is spaced apart from the rotating axis of the second gear 134.
As such, the power output of the engine unit can be transmitted to the axle 131 via a transmission line defined by the transmission belt 122, the driven pulley 121, the output shaft 120, the first gear 133, the third gear 134, the fourth gear 135, and the second gear 133′.
When it is desired to change the speed reduction ratio of the speed-changing unit 13, a fifth gear (not shown) is needed to be sleeved fixedly on the rotating shaft 132 to replace one of the third and fourth gears 134, 135 to mesh with a corresponding one of the first and second gears 133, 133′. Due to the addition of the fifth gear to the driving unit 12, it is necessary to increase the distance between the output shaft 120 and the axle 131 and, thus, the volume of the box 11. Hence, a new mold is required for manufacture of the box 11, thereby increasing the manufacturing costs of the first conventional vehicle transmission 1. Referring to FIG. 3, a second conventional vehicle transmission 2 includes a box 20, an output shaft 21, an axle 22, a rotating shaft 23 disposed at a central position 201 between the output shaft 21 and the axle 22, a first gear 24 sleeved fixedly on the output shaft 21, a second gear 25 sleeved fixedly on the axle 22, a third gear 26 sleeved fixedly on the rotating shaft 23 and meshing with the first gear 24, and a four gear 27 formed integrally on the rotating shaft 23 and meshing with the second gear 25. The rotating axes of the output shaft 21, the axle 22, and the rotating shaft 23 are aligned along a line (L′). Such an arrangement can be adjusted by moving the axle 22 and the rotating shaft 23 to the central position 201 and an upper position 202 located above the central position 201, respectively. Further rearrangement of the second conventional vehicle transmission 2, however, cannot be performed unless the size or structure of the box 11 is changed.